International Workshop on Imaging II

Neutron Tomography (NT) is an established technique to non-destructively investigate the inner structure of a wide range of objects. The major drawback of NT is the long acquisition time required to perform a tomographic scan compared to an X-ray Computed Tomography (CT) scan, due to the limited particle flux of the existing neutron sources. Therefore, in the NT field there is great interest in the reduction of scan time, dictated by the high neutrons production cost, aimed at optimizing the beamtime use at neutron imaging beamlines. A way for decreasing the total scan time is to reduce the number of projections. Generally, iterative reconstruction methods have advantages over analytical algorithms, such as the widely used Filtered Back-Projection (FBP), when data are noisy and limited. This research is focused on the comparative analysis of different reconstruction techniques, aimed at finding the data processing procedure suitable for NT, that reduces the scan time without reduction of the reconstructed image quality. For this purpose, a phantom sample was analysed by means of a white beam NT performed at the IMAT beamline, ISIS Neutron Source, U.K . Experimental data were used to test the performances of the FBP algorithm and different iterative reconstruction methods as a function of the number of projections and for different setups of the imaging system. The reconstructed images were quantitatively compared in terms of image quality indexes and the benefits of iterative methods for the limited data problem are discussed.

Milan Cathedral is one of the biggest and widest churches ever built among the other coeval architectures. It had a very long and complex construction history, which started in 1386 and lasted more than four centuries. The dominant style is the European gothic but the lombard tradition has strongly influenced the composition. Gothic cathedrals were diffusely built in Europe during the Middle Age, and each region developed its own local interpretation. However, a common feature of the style was the presence of slender pillars and of many elements able to reduce the horizontal thrusts of the vaults, such as spires, buttresesses, flying buttresesses and tie rods. In Milan Cathedral, tie rods have a fundamental role due to the specific characteristics of the structural system and its complex history. In 2012, a broken tie rod was found and it was substituted with a new one. Therefore, a multidisciplinary research on these elements started, aiming at a deeper material characterization and an in-situ identification of local defects. Among non-destructive techniques, several neutron analyses were performed on different samples. We will report on neutron diffraction measurements and neutron resonant capture analysis on part of the original broken tie rod. Moreover, neutron imaging was recorded on other iron tie rods (from an external spire). Results will be useful for an independent assessment and validation of models and of new on-site monitoring techniques, since no other conventional non-destructive technique will allow the same characterization.

The MCP-based neutron counting detector is a novel device that allows high spatial resolution and time-resolved neutron radiography and tomography with epithermal, thermal and cold neutrons. Time resolution is possible by the high readout speeds of ∼ 1200 frames/sec, allowing high resolution event counting with relatively high rates without spatial resolution degradation due to event overlaps. The electronic readout is based on a Timepix sensor, a CMOS pixel readout chip developed at CERN. Currently, a geometry of a quad Timepix detector is used with an active format of 28 × 28 mm² limited by the size of the Timepix quad (2 × 2 chips) readout. Measurements of a set of high-precision micrometers test samples have been performed at the Imaging and Materials Science & Engineering (IMAT) beamline operating at the ISIS spallation neutron source (U.K.). The aim of these experiments was the full characterization of the chip misalignment and of the gaps between each pad in the quad Timepix sensor. Such misalignment causes distortions of the recorded shape of the sample analyzed. We present in this work a post-processing image procedure that considers and corrects these effects. Results of the correction will be discussed and the efficacy of this method evaluated.

Synchrotron X-ray Phase Contrast micro-Tomography (SXrPCμT) is a powerful tool in the investigation of biological tissues, including the central nervous system (CNS), and it allows to simultaneously detect the vascular and neuronal network avoiding contrast agents or destructive sample preparations. However, specific sample preparation procedures aimed to optimize the achievable contrast- and signal-to-noise ratio (CNR and SNR, respectively) are required. Here we report and discuss the effects of perfusion with two different fixative agents (ethanol and paraformaldehyde) and with a widely used contrast medium (MICROFIL®) on mouse spinal cord. As a main result, we found that ethanol enhances contrast at the grey/white matter interface and increases the contrast in correspondence of vascular features and fibres, thus providing an adequate spatial resolution to visualise the vascular network at the microscale. On the other hand, ethanol is known to induce tissue dehydration, likely reducing cell dimensions below the spatial resolution limit imposed by the experimental technique. Nonetheless, neurons remain well visible using either perfused paraformaldehyde or MICROFIL® compound, as these latter media do not affect tissues with dehydration effects. Paraformaldehyde appears as the best compromise: it is not a contrast agent, like MICROFIL®, but it is less invasive than ethanol and permits to visualise well both cells and blood vessels. However, a quantitative estimation of the relative grey matter volume of each sample has led us to conclude that no significant alterations in the grey matter extension compared to the white matter occur as a consequence of the perfusion procedures tested in this study.

The biomedically focused brain research is largely performed on laboratory mice considering a high homology between the human and mouse genomes. A brain has an intricate and highly complex geometrical structure that is hard to display and analyse using only 2D methods. Applying some fast and efficient methods of brain visualization in 3D will be crucial for the neurobiology in the future. A post-mortem analysis of experimental animals' brains usually involves techniques such as magnetic resonance and computed tomography. These techniques are employed to visualize abnormalities in the brains' morphology or reparation processes. The X-ray computed microtomography (micro CT) plays an important role in the 3D imaging of internal structures of a large variety of soft and hard tissues. This non-destructive technique is applied in biological studies because the lab-based CT devices enable to obtain a several-micrometer resolution. However, this technique is always used along with some visualization methods, which are based on the tissue staining and thus differentiate soft tissues in biological samples. Here, a modified chemical contrasting protocol of tissues for a micro CT usage is introduced as the best tool for ex vivo 3D imaging of a post-mortem mouse brain. This way, the micro CT provides a high spatial resolution of the brain microscopic anatomy together with a high tissue differentiation contrast enabling to identify more anatomical details in the brain. As the micro CT allows a consequent reconstruction of the brain structures into a coherent 3D model, some small morphological changes can be given into context of their mutual spatial relationships.

Functional Magnetic Resonance Imaging (fMRI) based on Blood Oxygenation Level Dependent (BOLD) contrast has become one of the most powerful tools in neuroscience research. On the other hand, fMRI approaches have seen limited use in the study of spinal cord and subcortical brain regions (such as the brainstem and portions of the diencephalon). Indeed obtaining good BOLD signal in these areas still represents a technical and scientific challenge, due to poor control of physiological noise and to a limited overall quality of the functional series. A solution can be found in the combination of optimized experimental procedures at acquisition stage, and well-adapted artifact mitigation procedures in the data processing. In this framework, we studied two different data processing strategies to reduce physiological noise in cortical and subcortical brain regions and in the spinal cord, based on the aCompCor and RETROICOR denoising tools respectively. The study, performed in healthy subjects, was carried out using an ad hoc isometric motor task. We observed an increased signal to noise ratio in the denoised functional time series in the spinal cord and in the subcortical brain region.

Diagnostic imaging based on the Nuclear Magnetic Resonance phenomenon has increasingly spread in the recent few decades, mainly owing to its exquisite capability in depicting a contrast between soft tissues, to its generally non-invasive nature, and to the priceless advantage of using non-ionizing radiation. Magnetic Resonance (MR)-based acquisition techniques allow gathering information on the structure (through Magnetic Resonance Imaging— MRI), the metabolic composition (through Magnetic Resonance Spectroscopy—MRS), and the functioning (through functional MRI —fMRI) of the human body. MR investigations are the methods of choice for studying the brain in vivo, including anatomy, structural wiring and functional connectivity, in healthy and pathological conditions. Alongside the efforts of the clinical research community in extending the acquisition protocols to allow the exploration of a large variety of pathologies affecting diverse body regions, some relevant technological improvements are on the way to maximize the impact of MR in medical diagnostic. The development of MR scanners operating at ultra-high magnetic field (UHF) strength (⩾ 7 tesla), is pushing forward the spatial resolution of MRI and the spectral resolution of MRS, and it is increasing the specificity of fMRI to grey matter signal. UHF MR systems are currently in use for research purposes only; nevertheless, UHF technological advances are positively affecting MR investigations at clinical field strengths. To overcome the current major limitation of MRI, which is mostly based on contrast between tissues rather than on absolute measurements of physical quantities, a new acquisition modality is under development, which is referred as Magnetic Resonance Fingerprinting technique. Finally, as neuroimaging data acquired worldwide are reaching the typical size of Big Data, dedicated technical solutions are required to mine large amount of information and to identify specific biomarkers of pathological conditions.

We report on the application of the multi-aperture analyser X-ray Phase-Contrast imaging (XPCI) technique to the three-dimensional imaging of breast tissue samples. The experiment was conducted at the SYRMEP beamline (Elettra synchrotron, Italy) with a monochromatic X-ray beam. Along with the presentation of the methodology and resulting images, the potential extension of this approach to enable in-vivo applications at acceptable doses is discussed.

The word "theranostic" derives from the fusion of two terms: therapeutic and diagnostic. It is a promising research field that aims to develop innovative therapies with high target specificity by exploiting the therapeutic and diagnostic properties, in particular for metal-based nanoparticles (NPs) developed to erase cancer. In the framework of a combined research program on low dose X-ray imaging and theranostic nanoparticles (NPs), high resolution Phase-Contrast Tomography images of mice organs injected with gadolinium and gold-NPs were acquired at the European Synchrotron Radiation Facility (ESRF). Both compounds are good X-ray contrast agents due to their high attenuation coefficient with respect to biological tissues, especially immediately above K-edge energy. X-ray tomography is a powerful non-invasive technique to image the 3D vasculature network in order to detect abnormalities. Phase contrast methods provide more detailed anatomical information with higher discrimination among soft tissues. We present the images of mice liver and brain injected with gold and gadolinium NPs, respectively. We discuss different image processing methods used aiming at enhancing the accuracy on localizing nanoparticles.

IMAT is a new cold-neutron imaging facility at the neutron spallation source ISIS at the Rutherford Appleton Laboratory, U.K.. The ISIS pulsed source enables energy-selective and energy-resolved neutron imaging via time-of-flight (TOF) techniques, which are available in addition to the white-beam neutron radiography and tomography options. A spatial resolution of about 50 μm for white-beam neutron radiography was achieved early in the IMAT commissioning phase. In this work we have made the first steps towards achieving higher spatial resolution. A white-beam radiography with 18 μm spatial resolution was achieved in this experiment. This result was possible by using the event counting neutron pixel detector based on micro-channel plates (MCP) coupled with a Timepix readout chip with 55 μm sized pixels, and by employing an event centroiding technique. The prospects for energy-selective neutron radiography for this centroiding mode are discussed.